1. Technical Field
The presently disclosed subject matter relates to a light source device which uses a plurality of LED devices or the like as its light source. The presently disclosed subject matter also relates to a vehicle lighting device which uses this light source device, such as a headlight, an auxiliary headlight, tail-light, fog light, signal light, or the like.
2. Related Art
A conventional light source device utilizing an LED device has been known for use in a vehicle headlight, an LED lamp for use as a light source, and the like.
An example of a conventional vehicle headlight is disclosed in the Japanese Translation of PCT application No. 2003-503815 (corresponding to PCT Publication No. WO 01/001037) as shown in FIG. 1. The vehicle headlight of this type includes a light source which is composed of a plurality of light emitting diodes 1 arranged side by side, and an optical member (not shown) such as a lens located in front of the light source.
According to this configuration, the light emitted from the respective light emitting diodes 1 is given a distribution characteristic through the lens or other optical members arranged in front thereof, and is emitted outside. As a result, a desired light distribution property for the vehicle headlight is provided.
FIG. 2A shows a lighting device having an LED lamp as disclosed in Japanese Patent Application Laid-Open No. 2006-048934 (corresponding to U.S. Patent Publication No. 2006/022211A1). The lighting device includes an LED lamp 2 (see FIG. 2B) and a concave reflector 3. The LED lamp 2 is composed of a plurality of LEDs 2b which are arranged in a row on a substrate 2a so as to have an emission pattern similar to that of a filament type light emitting source. The reflector 3 is situated so that its focus lies near the light emitting point of the LED lamp 2.
According to this configuration, the light emitted from the LED lamp 2 is reflected by the reflector 3 and projected toward the front in the direction of light illumination. Consequently, the light emitting portion of the LED lamp 2 is projected forward with desired light distribution characteristics.
FIG. 3 shows another type of headlight disclosed in Japanese Patent Application Laid-Open No. 2001-076510. In contrast to the headlight and the lighting device described above utilizing LED devices, this headlight is configured to be a typical projector type headlight 4, which is composed of a bulb 5 as a light source, a reflector 6, a projection lens 7, and a light-shielding member 8.
The reflector 6 is composed of an elliptical reflecting surface whose first focus (rear focus) falls on or near the bulb 5 and whose major axis extends generally horizontally toward the front in the direction of light illumination. The inner side thereof constitutes the reflector.
The projection lens 7 is composed of a convex lens, or preferably an aspherical lens, and is arranged so that its focus on the light-source side (rear side) lies in the vicinity of the second focus of the reflector 6.
The light-shielding member 8 is intended to give the light projected forward a light distribution pattern for a predetermined low beam, and is arranged near the second focus of the reflector 6. The top edge 8a of the light-shielding member 8 is formed in a predetermined shape so as to create a cut-off line in the light distribution pattern.
Light emitted from the bulb 5 of the headlight 4 configured as described above is directly incident on the projection lens 7 and is then projected in the front illumination direction. Alternatively, the light is reflected by the reflector 6 to be focused near the second focus of the reflector 6 and the virtual image formed near the focus is reversed by the projection lens 7 to be projected in the front illumination direction.
On this occasion, part of the virtual image is shielded by the light-shielding member 8, so that the top edge 8a of the light-shielding member 8 forms a cut-off line C (see FIG. 4). The shaped virtual image is thus projected forward as a low beam.
It should be noted that when the virtual image shown in FIG. 4 is projected through the projection lens 7, the resulting light distribution pattern is vertically and horizontally reverse to the virtual image of FIG. 4, i.e., forms a light distribution pattern for right-side traffic. That is, the light distribution pattern has a luminance distribution such that the cut-off line C suppresses illumination from the center to the left in order to prevent any glare of light towards an opposite traveling vehicle.
As described above, vehicle lighting devices usually emit light with a light distribution pattern intended for a low beam (passing-by pattern), a high beam (traveling pattern), or the like. The light distribution pattern having a cut-off line C in particular will be defined as a cut-off pattern.
Japanese Patent Application Laid-Open No. 2004-233936 also describes a vehicle lamp apparatus. In particular, as shown in FIG. 5 of the Laid Open application, the apparatus includes an optical system for projecting light emitted from a light source toward the front in the direction of light illumination, along with two polarizing beam splitters, two half-wave plates, and other components which are arranged within this optical system. The light emitted from the light source (non-polarized light) is separated into p-polarized components and s-polarized components through the polarizing beam splitters. Assuming the s-polarized components to be a first perpendicular polarized beam, the p-polarized components are converted into a second perpendicular polarized beam through the half-wave plates, and these two perpendicular polarized beams are projected forward in the direction of light illumination.
By doing so, the light from the light source is separated into p- and s-polarized components, converted into respective perpendicular polarized beams, and projected forward in the direction of light illumination. Accordingly, it is possible to reduce reflection of light due to water particles when in heavy fog or in rain, thereby improving the visibility in front of the vehicle.
The vehicle headlight disclosed in Japanese Translation of PCT application No. 2003-503815 (corresponding to PCT publication No. WO 01/001037) includes a plurality of light emitting diodes 1 arranged side by side in order to provide a desired or required light intensity—enough for a lighting device.
A light source consisting of these juxtaposed light emitting diodes alone, however, cannot achieve a desired light distribution pattern.
In order to provide a desired light distribution pattern, it has thus been necessary to arrange an optical member for light distribution control in front of the light source.
Besides, this vehicle headlight is intended to improve the visibility around the vehicle, not to project light forward in the direction of light illumination to ensure the field of view for the driver of the vehicle.
In the lighting device having an LED lamp disclosed in Japanese Patent Application Laid-Open No. 2006-048934, a plurality of LED chips are built into one package in order to provide a light intensity required of the lighting device.
The light emitting area of this LED lamp, consisting of the plurality of LED chips, has the same shape as that of a conventional filament. Then, a reflecting surface for use in a projector type conventional headlight or the like is used to obtain a desired light distribution pattern.
In order to achieve a desired light distribution pattern, it has thus been necessary to arrange the reflector for light distribution control behind the light source, and a light-shielding member in front, if needed.
In this case, it is difficult, however, to achieve a desired light distribution pattern with only a single LED lamp. Consequently, the headlight must have a plurality of LED lamps, or have a so-called multi-lamp configuration, so that the size of the entire lighting device of the headlight becomes greater. The weight of the entire lighting device of the headlight also increases since the headlight should have a reflector.
This weight increase may not be preferable, especially for achieving the Adaptive Front-Lighting System (AFS) which has enjoyed recent popularity. This is because a large load is unfavorably applied to the drive mechanism in an AFS device.
In addition, since the LED lamps each contain a plurality of LED chips, the light emitting points of the respective LED chips may be visually observable in some cases. The resulting headlight provides a luminance distribution with small variations, whereby the appearance may deteriorate or not be desirable.
The headlight disclosed in Japanese Patent Application Laid-Open No. 2001-076510 also requires a reflector, and in some cases a light-shielding member inside the lighting device. The entire lighting device of the headlight therefore increases in size and in weight, with a depth as large as 130 mm or so, for example.
In addition, the reflector for use in this headlight has been designed so as to correspond to the shape of the light emitting portion of the light source bulb. It has thus taken a relatively long time to design such a reflector.
Now, under light distribution regulations and the like, typical vehicle lighting devices including those described in the foregoing patent documents are increasingly subject to control with respect to glare of light that is permissible on opposite traveling vehicles.
Specifically, European standards ECE (Reg. No. 98) and FMVSS define measuring points intended for controlling glare of light to opposite traveling vehicles in rainy weather. To be more specific, the measuring points are on the line of 4.29 D in accordance with ECE, and 4 D-4 R in accordance with FMVSS.
In terms of distance on the road, the measuring points are 9.3 m ahead in accordance with ECE, and 10 m ahead in accordance with FMVSS.
When in the rain, the road surface is usually covered with water films. As shown in FIG. 5A, the light L projected from a vehicle lighting device of the vehicle V is reflected forward at the surface of a water film W on the road.
At the position of incidence of the light L on the surface of the water film W, as shown in FIG. 5B, the angle of incidence θ1 and the angle of reflection θ2 are almost the same. Then, the reflected light L1 travels forward in a slightly upward direction.
In the meantime, as shown in FIG. 5B, light L2 that enters the water film W from the position of incidence on the surface of the water film W travels with a predetermined angle of refraction θ3 based on the refractive index of water until it reaches the road surface. This light L2 is then diffused by pits and projections of the road, and returns in part toward the vehicle V and reaches the driver. The driver can thus grasp, determine and understand the road condition.
In reality, however, most of the projected light L is reflected at the surface of the water film W as shown in FIG. 5A, so that the reflected light L1 travels forward in a slightly upward direction and causes glare of light to opposite traveling vehicles, pedestrians, and so on. This characteristics makes it difficult to meet the foregoing regulations on glare of light.
Furthermore, the vehicle lighting device as disclosed in Japanese Patent Application Laid-Open No. 2004-233936 can project perpendicular polarized light forward in the direction of light illumination, so that the scattering by water particles such as fog drips and raindrops in heavy fog or in rain is reduced to improve the visibility ahead.
The provision of perpendicular polarized light, however, requires a plurality of beam splitters each consisting or comprised of low refractive index films and high refractive index films deposited alternately, and a plurality of half-wave plates as well. As a result, the increased parts count and the complicated structure make the entire lighting device greater in size. This also requires complicated operations of aligning the optical axes of the optical components during assembly, thereby increasing the parts cost and the assembly cost.